Punch



J 1942. J. K. DUNCAN PUNCH Filed April 11, 1940 Patented June 23, 1942 PUNCH James K. Duncan, Chicago, Ill., assignor to United States Gypsum Company, Chicago, 11].,

a corporation of Illinois Application April 11, 1940, Serial No. 329,007 6 Claims. (Ci.164124) This invention relates to punches and has reference particularly to a punch which is especially adapted for perforating wet plasterboard, although it is also capable of use in the perforating of other material. It relates, moreover, to a punch adapted to be used in relatively high speed perforating machines.

The punching of wet plasterboard involves the overcoming of certain problems due to the material operated upon. In forming plasterboard a slurry or mix of gypsum or similar material is placed between two cover sheets of relatively heavy paper. It is, therefore, necessary to cut the cover sheets as well as to remove the core material in the perforating step. It is desirable to readily and cleanly cut the paper cover sheets and force the plug of material from the board without loosening the cover sheets from the plaster about the holes. The perforating is preferably done after the plaster has received its initial set and prior to the time it sets finally. In this condition the plaster is highly frangible, but not plastic to any extent, although wet or damp. 7

It is sometimes the practice in perforating wet plasterboard to employ a punch having a large cavity in its operating end which receives the plug of material as the punch is passing through the board. After the punch has passed completely through the board, additional means,

such as compressed air or a plunger, must be used to force the plug of material from the punch cavity. When punches of this type are employed they are generally forced through the plasterboard at relatively low speeds, such for instance as would result from the use of a rotary machine wherein the punches are arranged about a rotary punch carrier.

In another method the punches are forced through the board at relatively high speed, being carried by a rapidly moving reciprocating head. Punches for use in a relatively high speed machine of this type do not have a central cavity of a size to receive the plug of material, but force the plug out ahead of the punch.

The punches of the present invention are of the type which force the plugs of material cut from the plasterboard out ahead of the punch. In order to form a clean hole in the plasterboard the present punch is designed with a cutting edge which gradually slopes from the operating end of the punch at one side thereof toward the rear at the other side of the punch. By this means. the leading end of the punch readily pierces a small section of the top cover sheet and cutting edge thereof, after the initial penetration, cuts the top cover sheet-by a shearing action.

An object of the presentinvention is to provide a punch for punching wet plasterboard which will form clean, smooth holes without tearing the cover sheets.

Another object of this invention is to provide such a punch which may be employed in a relatively high-speed reciprocating perforating machine.

A still further object of the present invention is to provide a punch of simple design which may be readily produced.

Further objects and advantages will be apparent from the following description when considered with the drawing, in which:

Figure 1 is a cross-sectional view of one form of punch coming within the scope of the present invention, showing the manner in which the o'pcrating end is ground to'form asharp-cutting edge;

Fig. 2 is a side elevation of the type of punch shown in Figure l;

Fig. 3 is a side elevation ofanother type of punch in which the cutting edge is brought to a sharp point at its leading portion;

Fig. 4 is another side elevation of the punch shown in Fig. 3 when rotated 90; and

Fig. 5 is a fragmentary cross-sectional view speed reciprocating head. Beneath the punch is r a die 4 over which the plasterboard to be perforated is' fed. The die is provided with a flat work-supporting surface of suflicient area to support the board against the action of the punch and has a central opening 5 of a size to receive the punch I. Below the central opening there is an enlarged passage 6 which permitsthe plug of material removed from the plasterboard to fall freely therethrough.

The wet plasterboard comprises a top" cover sheet I and a bottom cover sheet 8, between which is the core of gypsum or plaster 9. The

as the punch advances through the board, the cover sheets I and 8 are generally'formed of multo the threaded end 2 of the plunger of the perforating machine in which it is to be used. Ordinarily it is desired to make the holes in the plasterboard round in cross section and a cylindrical shank is accordingly employed. However,

if other types of holes are to be formed, punches.

of suitable shape therefor may be provided. The operating or the lower end of the punch is formed with a sharp cutting edge l3, flush with the outer surface of the shank. The cutting edge slopes rearwardly or recedes from one side, indicated by ll, to the opposite side of the punch.

' The portion of the punch adjacent the cutting edge is beveled inwardl from the cutting edge to, or substantially to, the central passageway of the shank. The portion I5 of the beveled edge adjacent. the leading portion ll of the cutting edge forms a relatively acute angle with the outer surface of the shank. The sharpness of this angle gradually decreases from the leading portion of the punch to the portion I5 of the beveled edge at the opposite side thereof, where it is far less acute.

When a punch of the type shown in Figs. 1 and 2 is employed in perforating a sheet of wet plasterboard, as shown in Fig. 5, the leading portion H of the cutting edge |3 first pierces the top covering sheet I of the plasterboard. As the punch continues its downward movement, the cutting edge I3 completely shears the top paper cover while the leading portion of the punch is forced into the plaster. Because the beveled edge progressively becomes more flat toward the portion |B,-the plug is forced downwardly ahead of the punch. In order to further increase the thrust of the punch against the plug, a shoulder I! may 'be formed where the portion I5 of the beveled edge intersects the central opening of the shank.

Thus apunch of the type covered by my application serves two functions, namely, to easily and cleanly cut the top cover sheet of the plasterboard -and to force the plug out ahead of the punch and prevent its entry into the central opening.

In Figs. 3 and 4 I have illustrated a punch of another shape which also embodies the present invention. The tubular shank |8 thereof, instead of being rounded in cross section, is flattened on two sides, which intersect to form the edge l9. Itlikewise has a sharp cutting edge flush with the outer surface of the shank. The cutting edge 20 comes to a relatively sharp point 2| at the leading edge and recedes or slopes rearwardly therefrom toward the opposite side. The

beveled edge of this form of punch adjacent the point 2| formsv a relatively .acute angle with the outer surface of the shank and gradually flattens out toward the oppositeside of the punch, being flattest at the portion 22.

In operation, the punch illustrated in Figs. 3 and 4 works substantially the same as the punch shown in Figs. 1 and 2. The point 2| first pierces, the top covering I of the plasterboard and the cuttingedge thereafter shears the paper about the opening, and the beveled portion adjacent the cutting edge serves to force the plug ahead of the punch downwardly through the plasterboard and the die.

While it is possible that a small portion of the plug tends to enter the central opening in the shank, the beveled edge acts to prevent this, at least to the extent that the plug is readily thrown from the end of the punch when the limit of downward movement of the punch is reached. Therefore, no additional means are required to remove the plug from the punch.

The punches herelnbefore described are shown with substantially central openings extending therethrough'. This opening is not necessary for the operation of the punch as the plug of material is not received therein. However, it lightens the weight of the punch, which is desirable when it is rapidly reciprocating and facilitates its manufacture. Therefore, although it is generally preferable to have a central opening, it is not at all essential and the punch, if desired, may be solid,

To form the cutting edge of the punch and the beveled portion adjacent thereto, a grinding tool 23 is employed, which is substantially conical in shape, being preferably in the form of a truncated cone. The rotating grinder is held against the end of the shank, as shown in Fig. 1, with the axis of the grinder at a slight angle to the axis of the punch shank. -A portion of the grinder therefore extends into the central opening. Moreover, both in initially forming the sharp cutting edge on the punch and thereafter in sharpening it when it becomes dull, less grinding away of the metal is required due to the central opening in the punch. This facilitates the manufacture and maintenance of the punches.

It is therefore obvious that the punches of my invention may be readily manufactured, and in use will out clean perforations in the wet plasterboard, even when employed in relatively highspeed reciprocating machines.

While I have shown and described several modifications of my invention, it will be understood by those skilled in the art that various modifications thereof may be made without, departing from the spirit thereof, and therefore I wish to be limited only by the prior art and the scope of the appended claims.

I claim:

1. A punch of the class described comprising a tubular shank having a sharp cutting edge at its forward end substantially flush with the outer surface of said shank and sloping from one side thereof rearwardly toward the opposite side of said shank and the portion of the punch adjacent said cutting edge being beveled inwardly therefrom, said beveled surface extending from said cutting edge to the central opening in said shank and at the leading side of said punch forming a more acute angle with the surface of said shank than at the opposite side of the punch.

2. A punch for perforating wet plasterboard and the like comprising a tubular shank having a sharp cutting edge at its forward endsubstantially flush with the outer surface of said shank and sloping from one side thereof rearwardly toward the opposite side of said shank and the portion of the punch adjacent said cutting edge be ing beveled inwardly therefrom, said beveled surface extending from said cutting edge to the central opening in said shank and at the leading side of said punch forming a more acute angle with the surface of said shank than at the opposite side, and a shoulder portion formed on said beveled surface adjacent its intersection with the central opening in said shank.

3. The combination with a die having a fiat work-supporting surface of an appreciable area and a punch-receiving opening therein, of a punch of the class described comprising a shank having a sharp cutting edge at its forward end substantially flush with the outer surface of said shank and sloping from one side thereof rearwardly towards the opposite side, and the portion of the punch adjacent thereto being beveled inwardly from the cutting edge.

4. The combination with a die having a worksupporting surface and a punch-receiving opening therein, of a punch of the class described comprising a shank having a sharp cutting edge at its forward end substantially flush with the outer surface of said shank and sloping from one side thereof rearwardly towards the opposite side, and the portion of the punch adjacent thereto being beveled inwardly from the cutting edge, the beveled surface forming a relatively acute angle with the surface of said shank at the leading side of said punch and gradually becoming flatter at the opposite side of said punch.

5 at its forward end substantially flush with the outer surface of said shank and sloping from one side thereof rearwardly towards the opposite side, and the portion of the punch adjacent thereto being beveled inwardly in substantially straight 10 lines from the cutting edge, the beveled surface forming a relatively acute angle with the surface of said shank at the leading side of said punch and gradually becoming flatter at the opposite side of the punch.

6. A punch of the class described comprising a tubular shank having a sharp cutting edge at its forward end substantially flush with the outer {surface of said shank and sloping from one side thereof rearwardly toward the opposite side of said shank and the portion of the punch adjacent said cutting edge being beveled inwardly therefrom, said beveled surface extending in substantially straight lines fromjsaid cutting edge to the central opening in said shank and at the leading side of said punch forming a more acute angle with the surface of said shank than at the opposite side, of the punch.

; JAMES K. DUNCAN. 

